Theory of coherent transition radiation generated at a plasma-vacuum interface

Abstract

Transition radiation generated by an electron beam, produced by a laser wakefield accelerator operating in the self-modulated regime, crossing the plasma-vacuum boundary is considered. The angular distributions and spectra are calculated for both the incoherent and the coherent radiation. The effects of the longitudinal and transverse momentum distributions on the differential energy spectra are examined. Diffraction radiation from the finite transverse extent of the plasma is considered and shown to strongly modify the spectra and energy radiated for long-wavelength radiation. This method of transition radiation generation has the capability of producing high peak power terahertz radiation, of order 100 J/pulse at the plasma-vacuum interface, which is several orders of magnitude beyond current state-of-the-art terahertz sources.

Pulse shape and spectrum of coherent diffraction-limited transition radiation from electron beams

“…In the far-field (kR 1), and in the limit 1 1, the homogeneous solution in the region z ≥ 0 is found to be (Schroeder et al, 2004) 5) and Ψ j = k ⊥ · r ⊥,j + ωr z,j /v j . The unit vector e ⊥ is directed perpendicular to the vector of observation (k) in the k-ẑ plane, withẑ = (0, 0, 1).…”

“…Although the bunch charge is high, the fact that the transverse plasma size is on the order of 100-500 µm imposes a severe limitation on the intensity of the radiation. Theoretical work on the radiation characteristics of this THz source was reported by Schroeder et al (2004).…”

Advances in Laser Driven Accelerator R&D

“…[50] have the potential to resolve fs-bunches. Recently, the generation of coherent radiation from the electron bunches as they exit the plasma was studied experimentally [8,51] and theoretically [9], both as a radiation source and as a diagnostic for measuring the electron bunch properties [36]. The interest in using these bunches for generation of coherent radiation is motivated by two components: (1) extremely dense, sub-ps electron bunches produced with a compact laser-plasma accelerator and (2) the production of coherent transition radiation by these bunches at the boundary between a plasma and vacuum.…”

“…Over the years, the quality of these bunches improved, and beams were produced with "smaller" lasers, capable of operating at higher repetition rate. Laser pulse shape effects were studied [3,4], and applications were explored such as radio-isotope production [5,6,7] and THz radiation generation [8,9]. At AAC2002, experiments were reported, in which beams containing electrons with energy up to 200 MeV had been produced, using a 30 TW, 30 fs laser [10].…”

Laser guiding for GeV laser–plasma accelerators

“…The "smaller" lasers rely on Ti:Al 2 O 3 for amplifying medium and on chirped pulse amplification (Strickland and Mourou 1985) and are capable of producing 30 fs duration pulses containing several Joules of energy at a repetition rate of 10 Hz. Laser pulse shape effects were studied Schroeder et al 2003) (enabled by the CPA architecture of the laser), and applications were explored such as radio-isotope production (Santala et al 2001;Leemans et al 2001;Ledingham et al 2003), THz radiation generation (Leemans et al 2003;Schroeder et al 2004), and x-ray generation (Leemans et al 2000;Catravas et al 2001;Esarey et al 2002;Rousse et al 2004). Although steady progress had been made, the 100 percent energy spread remained a major limitation.…”